1. Field of the Invention
The present invention relates to a cylinder block of a multi-cylinder engine, and in particular a cooling water passage arrangement for such engine.
2. Explanation of Related Art
According to a technique proposed up to now, a spacing between adjacent cylinder bores is narrowed in order to make the multi-cylinder engine compact and light. Or a cylinder bore is formed larger than the conventional one to reduce the thickness of a wall between adjacent bores as much as possible so as to increase the exhaust amount in an attempt to enhance the output of the engine. Further, the proposed technique forms a cooling water passage within the wall between adjacent bores. For example, FIGS. 7 to 9 show a conventional technique proposed by an Assignee of the invention of the present application. Here, FIG. 7 is a vertical sectional view of a cooling water passage formed within a wall between adjacent bores, which is an essential part of a multi-cylinder block. FIG. 8 is a perspective view of a cylinder jacket core. FIG. 9(A) is a perspective view of a water passage forming member made of metal sheets. FIG. 9(B) is a plan view showing the water passage forming member filled with molding sand. FIG. 9(C) is a front view showing the water passage forming member filled with molding sand.
The conventional technique was disclosed, for example, in Japanese Patent Public Disclosure No. 8-319881. As shown in FIG. 7, a water passage forming member 110 made of metal sheets is embedded at a head side portion of an inter-bore wall 4 of a multi-cylinder block 1 by a molding process to form a cooling water passage 10. The metal sheet water passage forming member 110 comprises two molded metal sheet members joined to each other by welding or caulking as shown in FIG. 9(A).
The cooling water passage 10 comprises a pair of left and right rising water passages 12,12 having lower portions provided with cooling water induction portions 13,13, respectively, and a plurality of transverse water passages 15,15 provided in vertical and multiple stages for mutually communicating these rising water passages 12,12 as shown in FIG. 7. Cooling water within left and right cylinder jackets 8,8 is introduced from the cooling water induction portions 13,13 to a head jacket 22 through the transverse water passages 15,15 and the rising water passages 12,12 to thereby cool the head side portion of the inter-bore wall 4. A portion 11 of the water passage forming member 110 which does not form the cooling water passage 10 is welded to form a non-hollow portion. The metal sheet water passage forming member 110 is embedded into the inter-bore wall 4 by a molding process in the following manner.
As shown in FIGS. 9(B) and 9(C), there is preliminarily prepared a water passage forming member 110 filled with molding sand, which is attached to a position corresponding to an inter-bore wall of a jacket forming mold (not shown). The jacket forming mold is filled with molding sand under pressure by a core making machine to make a jacket core 30 as shown in FIG. 8. As such, the metal sheet water passage forming member 110 is integrated into the core 30. The metal sheet water passage forming member is employed because the conventional molding sand has insufficient flowability, filling ability and transverse rupture strength, and therefore is not suitable for forming the cooling water passage 10.
Next, the jacket core 30, a crank bore core (not shown), a cam balancer core (not shown) and the like are attached to a cylinder block forming metal mold (not shown), into which molten metal is poured. Then after the molten metal has been cooled, the sand is removed to finish the molding of the multi-cylinder block. As such, the metal sheet water passage forming member 110 is embedded into the inter-bore wall 4 by the molding process to form within the inter-bore wall 4 the cooling water passage 10 which communicates the cylinder jackets 8 with the head jacket 22.
According to the conventional technique, the metal sheet water passage forming member 110 is embedded into the inter-bore wall 4 by a molding process. This entails the following problems.
The jacket core 30 is different from the metal sheet water passage forming member 110 in expansion coefficient, which sometimes results in causing the jacket core 30 to crack and deform after molten metal has been poured.
Further, the metal sheet water passage forming member 110 is apt to insufficiently join with the poured molten metal. This causes the inter-bore wall 4 to distort when working the cylinder bore to result in separating the water passage forming member and ultimately decreasing the cooling effect due to reduction of thermal conduction between the water passage forming member and the inter-bore wall.
An attempt to sufficiently secure the working strength of the inter-bore wall 4 so as to be able to resist the distortion of the cylinder bore caused when working it invites a necessity of increasing the minimum thickness of the inter-bore wall 4. The sectional area of the cooling water passage 10 has to be decreased by an amount corresponding to the increase.
Then prior to the present invention, a trial was conducted to make the water passage forming member core of the molding sand which has been used up to now. But this molding sand is non-spherical and has a large spacing between sand particles to provide a bad filling ability and a weak mutual shape-retaining force. In consequence, in order to secure a strong mutual shape-retaining force and a desired transverse rupture strength, there is a need of enlarging the percentage content of a binder in the molding sand.
However, when the molding sand to make the water passage forming core has the percentage content of the binder enlarged, during the step of pouring the molten metal, if the binder vaporizes and splashes, it increases the generation of gas with the result of being apt to produce mold cavities. In addition, the water passage forming core has a smaller mass and calorific capacity than the other parts. Therefore, when the binder has vaporized and splashed, it extremely loses its shape-retaining force to collapse or the like due to pouring pressure and overheat, which eventually results in forming no water passage and causing, so-called, sand residue. In consequence, the molding sand is involved by the molding material and is seized onto the molded surface and the like to produce unuseful concave and convex portions which narrow the water passage. Additionally, water scale deposits on the concave and convex portions of an inner surface of the water passage to reduce the cooling efficiency.
The present invention provides a technique to form a cooling water passage by using a water passage forming core which is made of core sand to be mentioned later, instead of the conventional metal sheet water passage forming member, and has the following objects:
1. To solve the cracking or the like of a jacket forming core, attributable to the difference of expansion coefficient;
2. To solve a disadvantage of distorting the inter-bore wall when working the cylinder bore or the like;
3. To solve the problem of separation caused by the conventional technique and to enhance the cooling effect of the inter-bore wall;
4. To sufficiently secure the working strength of the cylinder bore and the sectional area of the cooling water passage; and
5. To solve the above-mentioned disadvantage which occurs when the water passage forming core is made of the conventionally used molding sand and to make a water passage forming core large in transverse rupture strength with a binder added in a small amount, thereby forming a highly accurate cooling water passage.
A cylinder block of a multi-cylinder engine as set forth in claim 1 has the following basic construction.
The multi-cylinder engine (E) has an inter-bore wall 4 whose head side portion is provided with a cooling water passage 10 having its molded surface disclosed. This cooling water passage 10 comprises a pair of left and right rising water passages 12,12 having lower portions provided with cooling water induction portions 13,13, respectively, and a plurality of transverse water passages 15 provided in vertical and multiple stages so as to communicate these rising water passages 12,12 with each other. Cooling water within left and right cylinder jackets 8,8 is introduced from the cooling water induction portions 13,13 into the cooling water passage 10 and then is flowed into a head jacket 22.
The invention has the following characteristic construction in order to accomplish the foregoing objects.
In the cylinder block of the multi-cylinder engine having the above-mentioned basic construction, there is provided between vertically adjoining transverse water pages 15, 15 a connecting portion 4b which connects a front half wall portion 4c of the inter-bore wall 4 to a rear half wall portion 4d thereof. The connecting portion 4b separates the vertically adjoining transverse water passages 15, 15 from each other. The cooling water passage 10 has its cast metal wall surface which faces a water passage space exposed in its entirety as a molded surface.
The invention is also characterized in that a molded surface of the cooling water passage 10 defines a portion of a wall surface of a cylinder jacket of the engine, and in that the portion of the wall surface of the cylinder jacket and the walls of the cooling passage are formed by casting metal around and against a water passage forming core made of sphered particle sand.
The invention forms a pair of left and right cylinder head tightening boss portions 5,5 in continuity with left and right opposite side portions of a head side portion 4a of the inter-bore wall 4 and arranges the cooling water induction portions 13, 13 in proximity to under surfaces of the boss portions, 5, 5, thereby vertically enlarging their openings and spreading them forwardly and rearwardly along with cylinder external peripheral surfaces 3b, 3b. 
The invention also contemplates a process of molding a cylinder block of a multi-cylinder engine comprises making a jacket core 30 so as to form cylinder jackets 8 of the multi-cylinder engine (E), attaching the jacket core 30 to a cylinder block forming mold 28, and pouring molten metal into the cylinder block forming mold 28.
The process uses a water passage forming core (31) of sphered particle sand having a lower expansion coefficient than the common silica sand, the core (31) being intended for forming at a head side portion of an inter-bore wall (4) of the multi-cylinder engine (E), a cooling water passage (10) which communicates the cylinder jackets (8) with a head jacket (22), and, prior to pouring the molten metal, it fixedly attaches the water passage forming core (31) to a position corresponding to the inter-bore wall (4) of the jacket core (30).
(a) According to the invention, in the cylinder block of the multi-cylinder engine having the foregoing basic construction, there is provided between vertically adjoining transverse water passages 15, 15 a connecting portion 4b which connects a front half wall portion 4c of an inter-bore wall 4 and a rear half wall portion 4d thereof to thereby separate the vertically adjoining transverse water passages 15, 15 from each other. This solves a disadvantage that the jacket core cracks or deforms due to the difference of expansion coefficient. This disadvantage was caused by the prior art which forms the water passage by embedding the metal sheet water passage forming member into the molding material.
(b) According to the invention as set forth in claim 1, the connecting portion 4b which connects the front half wall portion 4c of the inter-bore wall 4 and the rear half portion 4d thereof serves as a rib to reinforce the inter-bore wall 4 having the cooling water passage 10. This can solve another disadvantage that the inter-bore wall is distorted or the like when working the cylinder bore.
(c) The invention does not interpose the metal sheet water passage forming member. This solves the problem of separating the water passage forming member to result in enhancing the cooling effect of the inter-bore wall.
(d) The invention sets the height (H) of every transverse water passage 15 larger than the height (h) of the connection portion 4b. This can secure the sectional area of the cooling water passage sufficiently while obtaining the strength against the distortion of the cylinder bore caused when working it.
(e) According to the invention, in the cylinder block of the multi-cylinder engine, each transverse water passage 15 has a width (W) in a front and rear direction, set to between not less than ⅓ of a minimum thickness (T) of the inter-bore wall 4 and not more than ⅔ of the minimum thickness (T) and has a height (H) set to between not less than twice the height (h) of the connecting portion 4b and not more than three times the height (h). This can enlarge the sectional area of the cooling water passage much more to result in further enhancing the cooling effect of the inter-bore wall.
(f) In the cylinder block of the multi-cylinder engine, the invention forms a pair of left and right cylinder head tightening boss portions 5, 5 in continuity with left and right opposite side portions of a head side portion 4a and arranges a pair of left and right cooling water induction portions 13, 13 in proximity to under surfaces of the boss portions 5, 5. This can vertically enlarge openings of the cooling water induction portions 13, 13 toward the left and right cylinder jackets 8, 8. Beneath the boss portions 5, 5 the cylinder jackets 8, 8 are wide enough to flow the cooling water well. Accordingly, the cooling water within the cylinder jackets 8, 8 readily flows into the cooling water induction portions 13, 13 vertically and largely opened toward the cylinder jackets 8, 8. Besides, the openings of the induction portions 13, 13 are spread forwardly and rearwardly along the cylinder external peripheral surfaces 3b, 3b. Therefore, the cooling water smoothly flows along the cylinder external surfaces 3b to enter from the cooling water induction portions 13, 13 vertically and largely opened toward the cylinder jackets 8, 8 in a large amount. Then it passes through the cooling water passages 15 and the jacket communication passages 12, 12 to the head jacket 22 positioned above the inter-bore wall 4. Meanwhile, it strongly cools the head side portion 4a. This remarkably improves the cooling efficiency.
(g) According to the invention, in a process of molding the cylinder block of the multi-cylinder engine which has the foregoing basic construction, a water passage forming core (31) is made of sphered particle sand having a lower expansion coefficient than the common silica sand. The core (31) is intended for forming at a head side portion of an inter-bore wall (4) of the multi-cylinder engine (E), a cooling water passage (10) which communicates the cylinder jackets (8) with a head jacket (22). The sphered particle sand has an excellent flowability and filling ability. With a binder added in a small amount, it can make a water passage forming core having a large transverse rupture strength to result in the possibility of forming a highly accurate cooling water passage.
More specifically, when the water passage forming core is made of the conventionally used non-spherical molding sand, the non-spherical molding sand has so large a spacing between sand particles that it is not well filled and provides a weak mutual shape-:retaining force. Therefore, in order to secure a strong mutual shape-retaining force and a desired transverse rupture strength, a binder must be contained in the molding sand at a higher percentage. On the other hand, with the water passage forming core containing a binder at a higher percentage, during the molten metal pouring step, if the binder vaporizes and splashes, it emits more gas, which results in being apt to produce mold cavities at the spaces where the evaporative emission is made.
Besides, in the case where the water passage forming core which has a smaller mass and calorific capacity than the other parts is made of the conventional molding sand, when the binder has vaporized and splashed, it extremely loses its mutual shape-retaining force to collapse or the like due to pouring pressure and overheat and eventually to form no water passage and cause, so-called, sand residue. Therefore, the molding sand is involved by the molding material and is seized onto the molded surface and the like to produce unuseful concave and convex portions on an inner surface of the water passage, which narrow the water passage. Furthermore, water scale deposits on the concave and convex portion on the inner surface of the water passage to invite the reduction of the cooling efficiency.
On the other hand, the present invention has made the water passage forming core 31 of sphered particle sand having a lower expansion coefficient than the common silica sand. This sphered particle sand can secure the mutual shape-retaining force and the transverse rupture strength of the sand mold with a less binder content and prevent the seizing of the molding sand onto the molded surface. More specifically, it reduces the spacing between sand particles to largely improve its filling ability and strengthen the mutual shape-retaining force. In consequence, this can greatly decrease the percentage content of the binder to secure the mutual shape-retaining force and the desired transverse rupture strength. Along with this fact, even if the percentage content of the binder is 2.5% at weight ratio, the transverse rupture strength is increased to result in the possibility of forming a water passage forming core having such a high strength as the transverse rupture strength of 150 Kgf/cm2, which was considered difficult with the conventional non-spherical molding sand. In other words, even if the percentage content of the binder is largely reduced, it is possible to secure a sufficient mutual shape-retaining force and transverse rupture strength.
The water passage forming core 31 made of the sphered particle sand contains a binder in a small amount. Accordingly, at the molten metal pouring step, when the binder vaporizes and splashes, it emits less gas. This solves the problem of producing gaps and mold cavities at the portion where the evaporative emission is made. Further, even if the binder vaporizes and splashes, the molding sand has so strong a mutual shape-retaining force that it does not collapse nor cause, so-called, sand residue. In consequence, the molding sand is hardly involved by the molding material and is seldom seized onto the molded surface and the like to solve the disadvantage of narrowing the water passage and remove the deposit of water scale. In short, it is possible to form a highly accurate cooling water passage by using a water passage forming core which is made of sphered particle sand and has a transverse rupture strength large enough to be hardly broken.
(h) The invention fixedly attaches the water passage forming core 31 to a position corresponding to the inter-bore wall of the jacket core 30 prior to pouring the molten metal and therefore the cooling water passage 10 is formed with the water passage forming core 31. This solves the disadvantage of cracking and deforming the jacket core attributable to the difference of expansion coefficient. Such disadvantage was caused by the prior art which forms the water passage through molding the metal sheet water passage forming member embedded into the molding material.
(i) The invention does not interpose the metal sheet water passage forming member to solve the problem of separating the water passage forming member. Further, it can increase the sectional area of the cooling water passage 10 by an amount corresponding to the absence of the metal sheet water passage forming member and therefore can further enhance the cooling effect of the inter-bore wall.